The present invention relates to a sluice for discharging bulk material from a cyclone device, comprising a circumferential wall defining a generally cylindrical chamber with an inlet for receiving bulk material from the cyclone device, an outlet for discharging bulk material from the chamber, and a sluice wheel, which is rotatable in the chamber for sluicing bulk material in batches from the inlet through the chamber to the outlet.
Sluice devices of the above type maintain a counter pressure in the apex end of the cyclone device, through which the bulk material passes, so that the cyclone device works in the desired manner. In conventional sluices of this kind the sluice wheel rotates about a horizontal axis, wherein the inlet is situated on the top side of the circumferential wall for supplying the bulk material from the cyclone device radially to the sluice wheel and the outlet is situated on the underside of the circumferential wall for discharging the bulk material radially from the sluice wheel. The sluice wheel comprises radial sluice walls defining a number of cells evenly distributed around the horizontal axis of the sluice wheel. The radially outer ends of the sluice walls are provided with rubber seals sealing against the inner side of the circumferential wall, except when the sluice walls passes the inlet and the outlet during rotation of the sluice wheel.
A problem of such a conventional sluice is that bulk material with low density, such as fibers, poorly fills the cells of the sluice wheel, which reduces the capacity of the sluice. The rotational speed of the sluice wheel is limited to a relatively low value, since otherwise the influence of the centrifugal force on the bulk material in the cells of the sluice wheel will be great such that the bulk material simply is prevented from passing through the inlet of the sluice into the bypassing cells. For this reason the capacity of the sluice can not be increased by increasing the rotational speed of the sluice wheel. The solution to this capacity problem in connection with sluicing of bulk material with low density has been to install over-dimensioned, space demanding sluices, which are operated with low rpm.
Another problem of the conventional sluice is that long transition portions are required between the apex end of the cyclone device and the inlet of the sluice to prevent the vortex of the cyclone device from disturbing the filling of the cells of the sluice wheel with bulk material. For applications in which bulk material of fibers are dried in cyclone devices, such transitions portions may need to be up to seven meters long, as seen vertically.
A further problem of the conventional sluice is that the air leakage from the cyclone device through the sluice to the surroundings increases unsatisfactorily rapidly over time, because of the fact that the rubber sealings of the sluice walls age relatively rapidly. In addition, the rubber seals are worn out relatively rapidly because of the fact that material is jammed between the rubber seals and the circumferential wall when the rubber seals again seal against the circumferential wall after having passed the inlet during rotation of the sluice wheel.
One object of the present invention is to provide a sluice that eliminates the above mentioned problems of conventional sluices.
These and other objects of the present invention have now been realized by the invention of a sluice for discharging bulk material from a cyclone device, comprising a circumferential wall defining a generally cylindrical chamber having an inlet for receiving bulk material from the cyclone device and an outlet extending substantially tangentially to the cylindrical chamber for discharging bulk material therefrom, and a sluice wheel, which is rotatable in the chamber about a vertical axis extending through the center of the sluice wheel for sluicing the bulk material in batches from the inlet through the chamber to the outlet, wherein the inlet is located centrally above the sluice wheel for supplying bulk material substantially axially to the sluice wheel. In a preferred embodiment, the sluice wheel comprises a plurality of at least substantially radial sluice walls including radial inner and outer ends and distributed spaced apart from one another along the circumference of the sluice wheel, the sluice walls abutting sealingly with the radial outer ends against the circumferential wall except at the outlet, and the radial inner ends of the sluice walls are situated at a predetermined distance from the center of the sluice wheel, so that a central free space communicating with the inlet is formed in the sluice wheel. In a preferred embodiment, the sluice wheel comprises a lower circular gable wall and an upper annular circular gable wall, and the sluice walls extend axially between and are connected to the lower and upper gable walls.
In accordance with a preferred embodiment of the apparatus of the present invention, the sluice further comprises a stationary partial cylindrical wall extending in the central space coaxially with the sluice wheel and abutting sealingly against the upper and lower gable walls, wherein the partial cylindrical wall extends past the outlet as seen in the circumferential direction of the sluice wheel. In a preferred embodiment, the radial outer end of each sluice wall abuts sealingly against the circumferential wall except when the sluice wall passes the outlet during rotation of the sluice wheel. In a preferred embodiment, the circumferential wall comprises a curved bendable band including an end which is fixed against movement in the longitudinal direction of the band and an opposite end which is movable in the longitudinal direction of the band for adjustment of the radial extension of the band. Preferably, the opposite end of the band is connected to a pre-stretched draw spring for automatic adjustment of the radial extension of the band, so that a satisfactory sealing between the band and the radial outer ends of the sluice walls is achieved during operation.
In accordance with another embodiment of the apparatus of the present invention, the radial inner end of each sluice wall abuts sealingly against the partial cylindrical wall when the partial cylindrical wall is passed by the sluice wall during rotation of the sluice wheel. Preferably, the partial cylindrical wall has an extension in the circumferential direction of the sluice wheel such that at least one sluice wall seals between the circumferential wall and the partial cylindrical wall at each side of the outlet, as seen in the circumferential direction, independent of the turning position of the sluice wheel.
The objects of the present invention are obtained by a sluice in which the sluice wheel is rotatable about a vertical axis extending through the center of the sluice wheel, that the inlet is situated centrally above the sluice wheel for supplying bulk material substantially axially to the sluice wheel, and that the inlet extends substantially tangentially to the cylindrical chamber. By the fact that the bulk material is axially received by the sluice wheel the influence by the centrifugal force on the bulk material will give the favorable consequence that the bulk material will be packed radially outwardly in the sluice wheel, which gives the sluice according to the present invention a good capacity. In addition, the vortex of the cyclone device can be allowed to extend through the inlet all the way into the sluice wheel without disturbing the filling of the sluice with bulk material, which has the consequence that the length of the transition portion between the cyclone device and the sluice can be made relatively short. For instance, the transition portion needs only be about four meters in length when sluicing bulk material in the form of fibers, which compared to a corresponding transition portion in a conventional sluice means a reduction in length of about 40%. Since the sluice walls of the sluice wheel always abut with their radially outer seals against the inner side of the circumferential wall at the area of inlet, the risk of the bulk material jamming between said seals and the circumferential wall is significantly reduced.
Preferably, the sluice wheel comprises a plurality of at least substantially radial sluice walls, which are distributed spaced from one another along the circumference of the sluice wheel and which with their radial outer ends abut sealingly against the circumferential wall, except at the outlet. The radial inner ends of the sluice walls are suitably situated at a predetermined distance from the center of the sluice wheel, so that a central free space communicating with the inlet is formed in the sluice wheel.
In accordance with a simple design of the sluice wheel it comprises a lower circular gable wall and an upper annular circular gable wall, wherein the sluice walls extend axially between and are connected to the lower and upper gable walls. The lower gable wall may suitably be connected to a drive motor.
To achieve a good air sealing between the central space and the outlet the sluice according to the present invention comprises a stationary part-cylindrical wall extending in the central space coaxially with the sluice wheel and abutting sealingly against the upper and lower gable walls, wherein the part-cylindrical wall extends past the outlet as seen in the circumferential direction of the sluice wheel. Suitably the radially inner end of each sluice wall abuts sealingly against the part-cylindrical wall when the latter is passed by the sluice wall during rotation of the sluice wheel, while the radially outer end of each sluice wall abuts sealingly against the circumferential wall except when the sluice wall passes the outlet during the rotation of the sluice wheel.
The part-cylindrical wall has such an extension in the circumferential direction of the sluice wheel that at least one sluice wall seals between the circumferential wall and the part-cylindrical wall on each side of the outlet, as seen in circumferential direction, independent of the turning position of the sluice wheel.
The circumferential wall may comprise a curved bendable band with one end fixed against movement in the longitudinal direction of the band and with one opposite end which is moveable in the longitudinal direction of the band for adjustment of the radial extension of the band. As a result, when required the band can be adjusted concurrently with the wear of the radial outer ends or seals of the sluice walls. The opposite ends of the band are advantageously connected to a pre-stretched draw spring or air cylinder for automatic adjustment of the radial extension of the band, so that a satisfactory sealing between the band and the radially outer ends of the sluice walls are achieved during operation. Alternatively, a circumferential wall may of course be stationary and the radially outer ends of the sluice wall may be provided with conventional sealing rubber lips.